The present invention relates to a die that is employed in a device for manufacturing nonwoven fabric using a melt-blowing method to spin molten plastic.
Conventionally, nonwoven fabric manufactured by a melt-blowing method is used, for example, for filtering material of a cabin air filter for a vehicle.
As shown in FIG. 10, a device for manufacturing nonwoven fabric using a melt-blowing method includes a die 90 for spinning molten plastic 95, a conveyor 93, which is arranged below the die 90, and a roller 94. The conveyor 93 collects a spun fiber 96 and conveys the fiber 96. The roller 94 rolls the nonwoven fabric 97, which is collected by the conveyor 93 and thus formed into a band shape.
In the die 90, the molten plastic 95 that has been extruded from a non-illustrated extruder is discharged downward from a discharge port, which opens in the lower surface of the die 90, through a plastic passage 91. Hot air flow 98, which is supplied from a non-illustrated hot air flow generating device, is blown from blowing ports, which open in the lower surface, through hot air passages 92 formed on the opposite sides of the plastic passage 91. The hot air flow 98 blown from the blowing ports is blown onto the molten plastic 95, which is discharged from the discharge port. The molten plastic 95 is thus drawn into the form of fiber to decrease the diameter of the fiber 96.
In the die disclosed in Japanese Laid-Open Patent Publication No. 2012-180611, an annular blowing port is arranged around each of the discharge ports, which blow molten plastic. The molten plastic 95 is thus fully surrounded by hot air flow blown from the blowing port.
To increase the velocity of manufacturing nonwoven fabric in the step of manufacturing the nonwoven fabric 97 using the melt-blowing method, the conveying speed of the conveyor 93 must be increased. However, if the conveying speed of the conveyor 93 is increased, the weight per unit area of the nonwoven fabric 97 is decreased. To maintain the weight per unit area of the nonwoven fabric 97, the discharge amount of the molten plastic 95 must be increased. However, to increase the discharge amount of the molten plastic 95, the molten plastic 95 must be heated to increase flowability. This increases the diameter of the discharged molten plastic 95, thus increasing the diameter of the fiber 96. To prevent such increase of the fiber diameter, the flow amount of the hot air flow 98 for drawing the molten plastic 95 must be increased. However, if the flow amount of the hot air flow 98 is increased, turbulence in airflows in the vicinity of the fiber 96 is promoted. As a result, in the conventional die 90, as well as the die disclosed in Japanese Laid-Open Patent Publication No. 2012-180611, fusion among the fibers 96 is promoted while the fibers 96 move from the die 90 to the conveyor 93, as shown in FIG. 11. The fibers 96 thus tend to form bundles each formed by multiple fibers 96. This may lower the clogging performance of the nonwoven fabric 97, that is, may lower the total amount of dust collected before the nonwoven fabric 97 becomes clogged.